The present invention relates to water soluble photoresist compositions which are based on a simultaneous cationic and free radical cure of a blend of an alkanolacrylamide and a water soluble hydroxyl containing film forming organic oligomer in combination with an onium salt, such as a triarylsulfonium salt, or a diaryliodonium salt.
Prior to the present invention, as shown by Barton, U.S. Pat. No. 4,090,936, photohardenable liquid compositions were provided which were useful as photoresists and consisted of epoxy resin in combination with a polyvinylformal or polyvinylbutyral resin and an effective amount of photoinitiator, such as an aromatic sulfonium salt or aromatic iodonium salt. The photocurable compositions of Barton are based solely on a cationic cure and utilize an organic solvent to develop the unexposed areas of the photoresist employed in the form of a dry film. In U.S. Pat. No. 4,245,029, Crivello, assigned to the same assignee as the present invention, photocurable compositions are shown useful as metal coatings having improved solvent resistance based on the simultaneous free-radical cure and cationic cure of an organic resin mixture. These photocurable compositions utilize a triarylsulfonium salt as a photoinitiator for oxirane containing monomeric or polymeric organic material in combination with an aliphatically unsaturated organic material free of oxirane oxygen. The resulting cured compositions have been found to possess improved solvent resistance as metal coatings.
The present invention is based on the discovery that water soluble blends of alkanolacrylamide, water soluble hydroxyl containing film forming organic oligomer, for example, certain polyvinylalcohols and an effective amount of an onium salt photoinitiator, such as a diaryliodonium salt, or triarylsulfonium salt can be converted to a photocurable film useful as a photoresist. A simultaneous free radical and cationic cure of the exposed portions of the dry film can be readily achieved. The resulting patterned dry film photoresist can then be readily developed in hot water resulting in a finely patterned negative image of the mask.